(1) Field of the Invention
The present invention relates generally to an apparatus for feeding a continuous stream of material into a plurality of packages or other receptacles, and in particular to an apparatus for measuring the weight of material being fed and diverting the material stream from a first pathway to a second pathway when a predetermined weight of material is measured.
(2) Description of the Prior Art
Numerous solid particulate materials are packaged in receptacles for sale to the ultimate consumer or to a downstream processor. A brief exemplary listing of such materials include plastic and metal components and parts; food items, such as cereals, corn meal, rice, spices, soybeans, and potato chips; and a variety of other materials, such as tobacco, plastic pellets, etc. Exemplary receptacles include boxes, containers, pouches, packages, cartons, and bags.
Generally, the material is fed as a continuous or discontinuous feed from a bulk supply source, such as a hopper, directly into the receptacles, or into intermediate collection hoppers for transfer into the receptacles. The apparatus used to transfer the material from the supply source into the individual receptacles may vary dependent upon the type of material, but will normally include a means for weighing the material at some point between the supply source and the receptacle or within the actual receptacle, with some feed-back being provided to control the feed rate, and thereby the amount of material being fed into a given receptacle during a given time period. Control of the feed rate is used not only for material packaged by weight, but also for items packaged by the number of items, since these latter items are frequently packaged on the basis of the weight of the number of items in a package, as opposed to counting the number of items packaged.
In some types of apparatus used to discharge material into a plurality of receptacles, a continuous stream of the material is fed from a bulk supply source, such as a bulk hopper onto a weigh conveyor, and then discharged from the conveyor along a first pathway into a first receptacle. The weight of material conveyed into the first receptacle is measured, either by weighing the amount of material being conveyed, or the weight of the receptacle. When the desired weight is reached, the material stream is diverted along a second pathway, e.g., by a diverter, to feed the stream into a second receptacle. Alternatively, the first and second streams can be fed into intermediate hoppers with the material within a hopper being discharged into a receptacle when the desired weight has been reached. In many instances, a weigh conveyor is used to measure the weight of material being carried on the conveyor during a given time, thereby indicating the weight of material fed to the receptacle.
For production efficiency, some materials are fed continuously at a high rate of feed, with up to the order of 600 packages per minute being filled. Unfortunately, existing filling systems do not measure the material with a high degree of accuracy, particularly at these higher feed volumes. Additionally, mechanisms currently used to divert a stream from one pathway to another do not respond at these speeds with sufficient rapidity to accurately fill the receptacles with the correct weight of material. Therefore, there is a continuing need for an apparatus for accurately dispensing solid particulate material from a bulk supply source into a plurality of receptacles based on the weight of the material being dispensed.
The present invention addresses this need by providing an improved apparatus for continuously and accurately weighing a continuous feed of solid particulate material, and rapidly diverting the stream of material from a first pathway to a second pathway, and thereby from a first receptacle to a second receptacle, responsive to the measurement of a target weight. Generally, the present invention is comprised of a dynamic measurement device in combination with a stream diverter and control circuitry to rapidly actuate the diverter in response to weight measurements. Particularly suitable dynamic measurement devices are described in earlier U.S. Pat. No. 5,219,031, issued Jun. 15, 1993, and U.S. Pat. No. 5,230,251, issued Jul. 27, 1993, to the present inventor. The apparatus may also include means to control material feed and/or receptacle positioning responsive to weight or material flow measurements.
Generally, the dynamic measurement device is comprised of a curved weigh pan having inlet and outlet ends, and an inwardly curved surface extending between the pan ends. The pan is positioned to receive a continuous stream of solid particulate material tangentially at the inlet end, i.e., the material stream is directed substantially perpendicular to the radius of curvature of the pan at the upper end. As a result, the material flows around the curved surface of the pan without impacting the pan, eliminating errors due to the movement of the pan under impact forces.
The pan is mounted on the distal end of an elongated support arm, with the proximal end of the arm being attached to a suitable support at a distance from the pan. To permit pan displacement, the arm is either flexible or is pivotally attaching at its proximal end. When material flows over the inwardly curved pan, an inward centripetal force, and a corresponding outward force, is exerted causing the pan to move outwardly. This outward movement, corresponding to the weight, or change in weight, of the material moving across the pan is measured by the displacement measurement instrument. A displacement measurement instrument, such as a transducer, is positioned to measure the displacement of the pan.
Since the outward force exerted against the pan is due entirely to the centripetal force, and is independent of any impact or frictional forces, measurement is highly accurate, and can be measured instantaneously. For optimal measurement independent of non-centripetal force factors, the pivot point of the arm is preferably located so that a line extending from the arm to the pan approximately midway between the pan inlet and outlet ends is perpendicular to the radius of curvature of the pan.
In the present apparatus, the dynamic measurement device is combined with a material feeder to direct particulate material tangentially along the inner surface of the pan at its inlet end, and a diverter positioned adjacent the outlet end of the pan. Generally, the diverter includes an inner end toward the pan, a pivotal outer end, an upper surface tangentially aligned with the pan surface at pan outer end, preferably along a substantially horizontal plane, and a lower surface that preferably diverges from the inner end of the diverter and includes an inlet end, an outlet end, and a downwardly curved lower surface between the ends.
The diverter includes a diverter actuator to pivot the diverter about its outer end between a lowered position in which the upper surface of the diverter is parallel to the tangent of the outer end of the pan, and a raised position in which the lower surface of the diverter intersects the tangent of the lower end of the pan. The actuator can be a stepping motor, a solenoid, or one of several other devices known to one skilled in the art to be suitable for this purpose, the only requirement being its capability to rapidly pivot the diverter.
When the diverter is in the lowered position, material discharged from the pan will pass along a first pathway over, and preferably in contact with, the upper surface of the diverter. However, when the diverter is raised, the material flows across the lower surface of the diverter and along a second pathway. When in the raised position, the inner end of the diverter extends slightly above the upper surface of the material stream, so that the material flow is substantially tangential to the radius of curvature of the diverter lower surface at its inlet end, thereby creating a smooth flow of material against the diverter lower surface.
Material flowing along the first and second pathways is received by material receptacles positioned along the pathways. The material receptacle may be the final receptacle, with a new receptacle being positioned within the pathway upon completion of filling of a given receptacle. For example, a series of receptacles may be moved on a conveyor beneath a pathway. The conveyor may move intermittently or continuously. Alternatively, the material receptacle can be an intermediate hopper that is filled with material that is later discharged into the final receptacle when the desired amount is in the hopper.
In order to achieve the desired level of fill accuracy, the amount of material flowing along a given pathway, either the first or second pathway, during a given time must be accurately measured, and the material flow must be rapidly switched from the given pathway to the other pathway when a predetermined amount of material has been discharged. This result is achieved by comparing measured weight, determined by pan displacement over time, against a predetermined target weight. Generally, the apparatus includes a controller or processor to receive displacement information from the transducer or other displacement measurement instrument. The controller then calculates the cumulative weight of material fed over the pan and transmits a signal when a target weight is reached.
In operation, a continuous feed of solid particulate material is directed onto the weight pan tangential to the pan inlet end. The material moving across to pan surface is discharged from the pan outlet end along a first pathway across the upper surface of the diverter. As the material moves across the pan, the pan is deflected slightly outwardly by centripetal force. This deflection is measured by the transducer or other deflection measurement instrument. The controller receives measurement information from the deflection measurement instrument, and calculates the cumulative weight of material moving along the first pathway during a given fill sequence.
When a target cumulative weight is reached, the controller signals the actuator to pivot the diverter to the raised position. The actuator then quickly pivots the diverter inner end upwardly through the material stream, causing the stream to flow against the lower surface of the diverter and along a second pathway. Material flow along the second pathway is then undertaken until the target weight is reached, at which time the diverter is pivoted to the lowered position. Material discharged along the first or second pathway is collected into the final receptacles, or into intermediate hoppers. Surprisingly, it has been found that discharge of the material from the curved weigh pan combined with insertion of the adjacent diverter upwardly through the stream results in highly rapid diversion of the stream between pathways, and resulting highly accurate filling of receptacles.